1. Field of the Invention
The present invention relates to a scroll compressor which is installed in an air conditioner, a refrigerator, or the like, and in particular, a scroll compressor comprising characteristic scroll members.
2. Description of the Related Art
In conventional scroll compressors, a fixed scroll and an orbiting scroll are provided by engaging their spiral wall bodies, and fluid inside a compression chamber, which has a crescent shape and is formed between the spiral wall bodies, is compressed by gradually reducing the volume of the compression chamber as the orbiting scroll revolves around the fixed scroll.
The compression ratio in the design of the scroll compressor is determined based on the ratio of the maximum volume of the compression chamber (the volume at the point when the compression chamber is formed by the engaging of the spiral wall bodies) with respect to the minimum volume of the compression chamber (the volume immediately before the spiral wall bodies become unengaged and the compression chamber disappears). Conventionally, in order to increase the compression ability of the scroll compressor, the number of windings of the spiral wall bodies of both scrolls is increased, and thereby the cross-sectional area of the compression chamber at maximum volume is increased. However, in the conventional method of increasing the number of windings of the spiral wall bodies, the external shape of the scrolls is enlarged, increasing the size of the compressor; for this reason, it is difficult to use this method in an air conditioner for vehicles and the like which have strict size limitations.
In an attempt to solve the problem, the publication of Japanese Patent No. 1296431 proposes the following scroll compressor comprising stepwise scroll members.
FIG. 4A shows a fixed scroll 1 of the above patent comprising an end plate 1a and a spiral wall body 1b provided on one side surface of the end plate 1a. FIG. 4B shows an orbiting scroll 2 similarly comprising an end plate 2a and a spiral wall body 2b provided on one side surface of the end plate 2a. 
A step portion 3 is provided on the surface of the end plate 1a of the fixed scroll 1. The step portion 3 has two parts in which one is a high part at the center of the surface of the end plate 1a and the other is a low part at the outer end of the end plate 1a. Furthermore, a step portion 4, corresponding to the step portion 3 of the end plate 1a, is provided in the spiral wall body 1b of the fixed scroll 1. The step portion 4 has two parts in which one is a low part at the center of the spiral wall body 1b and the other is a high part at the outer end of the spiral wall body 1b. Similarly, a step portion 3 is provided on the surface of the end plate 2a of the orbiting scroll 2. The step portion 3 has two parts in which one is a high part at the center of the surface of the end plate 2a and the other is a low part at the outer end of the end plate 2a. Furthermore, a step portion 4, corresponding to the step portion 3, is provided in the spiral wall body 2b of the orbiting scroll 2. The step portion 4 has two parts in which one is a low part at the center of the spiral wall body 2b and the other is a high part at the outer end of the spiral wall body 2b. 
FIG. 5 shows the state when the spiral wall body 1b of the fixed scroll 1 and the spiral wall body 2b of the orbiting scroll 2 are engaged. While this engagement state is maintained, the orbiting scroll 2 is revolved eccentrically with respect to the fixed scroll 1, and the volume of compression chambers C1 to C5, which are formed by the spiral wall bodies 1b and 2b, gradually decreases. Thereby, fluid in the compression chambers C1 to C5 is gradually compressed, and finally the fluid is discharged at a high pressure from a discharge port 5 provided at the center of the end plate 1a of the fixed scroll 1. In the scroll compressor comprising such a structure, since the volume of the compression chamber suddenly decreases because of the existence of the step portions 3 and 3, the minimum volume in the compression chambers can be reduced. Thereby, without an increase in the size of both the fixed scroll 1 and the orbiting scroll 2, the compression ratio can be improved.
However, in the scroll compressor comprising the fixed scroll 1 and the orbiting scroll 2 comprising the step portions 3 and 3, a tip clearance (not shown in figures) is formed between the end plate 1a of the fixed scroll 1 and the top edge of the spiral wall body 2b of the orbiting scroll 2, and between the end plate 2a of the orbiting scroll 2 and the top edge of the spiral wall body 1b of the fixed scroll 1. If the tip clearance is too small, the smooth revolution of the orbiting scroll 2 with respect to the fixed scroll 1 is inhibited, and a power increase may be caused. In addition, when the scroll compressor is operated at high temperatures, the spiral wall bodies 1b and 2b of the fixed scroll 1 and the orbiting scroll 2 expand, the top edge of the spiral wall bodies 1b and 2b and the end plates 1a and 2a make firmly contact, and thereby, abrasion or seizure may occur.
Furthermore, as described above, since the volume of the compression chambers suddenly decreases due to the existence of the step portions 3 and 3, the differential pressure between in the compression chambers at the center and the compression chambers at the outer end, with respect to the step portions 3 and 3 is relatively large.
In contrast, if the tip clearance is too large, the amount of leakage of the compressed gas, which flows via the tip clearance between the adjacent compression chambers increases, and there are cases in which the compression ability of the scroll compressor is degraded.
Therefore, it is necessary for the tip clearance to be adjusted in a suitable range. In conventional scroll compressors, a tip clearance at any position in the spiral direction of the spiral wall bodies 1b and 2b is adjusted to a substantially fixed value. In other words, if the tip clearance between the end plates 1a and 2a and the top edge of the spiral wall bodies 1b and 2b at the low part of the end plates 1a and 2a (outer end of the end plates 1a and 2a with respect to the step portions 3 and 3) is defined as xcex41, and the tip clearance between the end plates 1a and 2a and the top edge of the spiral wall bodies 1b and 2b at the high part of the end plates 1a and 2a (center position of the end plates 1a and 2a with respect to the step portions 3 and 3) is defined as xcex42, in conventional scroll compressors, the relation xcex41=xcex42 is established.
However, in order to satisfy the relation xcex41=xcex42, it is necessary to improve the working precision of the fixed scroll 1 and the orbiting scroll 2, and measure xcex41 and xcex42 during the assembly processes. A large number of man-hours is required, and an increase in the cost cannot be avoided.
In consideration of the above-described problems, it is an object of the present invention to provide a scroll compressor which can improve the decrease in the compression ratio due to the leakage of compressed gas via the tip clearance between the adjacent compression chambers, which can be assembled with a fewer processes, and which can be manufactured at a low cost.
One aspect of the present invention is a scroll compressor comprising a fixed scroll member which is fixed in position and has a spiral wall body provided on one surface of an end plate; an orbiting scroll member which has a spiral wall body provided on one surface of an end plate, being supported by engaging the spiral wall bodies so as to orbit and revolve around the fixed scroll member without rotation; the spiral wall bodies of the fixed scroll member and the orbiting scroll member each comprise a step portion which divides a top edge of the spiral wall body into plural parts forming a low top edge at the center and a high top edge at the outer end of the spiral wall body; and the end plates of the fixed scroll member and the orbiting scroll member each comprise a step portion which divides the end plate into a high part at the center and a low part at the outer end of the end plate; wherein at least one of a clearance between the high part of the end plate of the fixed scroll member and the low top edge of the spiral wall body of the orbiting scroll member, and a clearance between the high part of the end plate of the orbiting scroll member and the low top edge of the spiral wall body of the fixed scroll member is a fixed value.
According to this scroll compressor, since the scroll compressor is assembled only by adjusting a clearance xcex42 between the high part of the end plate and low top edge of the spiral wall body to a fixed value, the working of the fixed scroll member and the orbiting scroll member is easy and the assembly of the scroll compressor is relatively easy.
In the scroll compressor, when the tip clearance between the low part of the end plates and the high top edge of the spiral wall bodies corresponding to the low part is defined as xcex41, and the tip clearance between the high part of the end plates and the low top edge of the spiral wall bodies corresponding to the high part of the end plates is defined as xcex42, it is preferable to establish the relation xcex41 less than xcex42.
Here, the tip clearances xcex41 and xcex42 during operation are defined as xcex41d and xcex42d. As described above, during operation, the volume of the compression chambers at the center with respect to the step portion suddenly decreases, and the pressure of the compression chambers suddenly increases. Therefore, in the temperature distribution of the scroll members, the temperature at the center of the scroll members is higher than that at the outer end of the scroll members.
In other words, due to expansion by heat of the scroll members, the tip clearance xcex42d at the high temperature side during operation, that is, the tip clearance xcex42d at the center of the scroll members during operation, is smaller than the tip clearance xcex42 which is determined in the assembly process.
In contrast, since the tip clearance xcex41d at the outer end of the scroll members during operation does not decrease as compared with the tip clearance xcex42d at the center of the scroll members, the tip clearances xcex41d and xcex42d during operation level off, and an excellent performance for scroll compressors can be obtained. That is, it is possible to prevent the leakage of the compressed gas and to improve the refrigeration ability.
In addition, in the scroll compressor, it is preferable for a groove to be formed on the top edge of the spiral wall bodies, for a tip seal for sealing the border between the top edge of the spiral wall bodies and the end plates which are opposite the spiral wall bodies to be fit into the groove, and for at least one of a tip seal which is fit into the groove on the high top edge of the spiral wall body of the orbiting scroll member corresponding to the low part of the end plate of the fixed scroll member, and another tip seal which is fit into the groove on the high top edge of the spiral wall body of the fixed scroll member corresponding to the low part of the end plate of the orbiting scroll member, protrudes from the high top edge of the spiral body.
According to the scroll compressor, a tip seal for sealing the border between the top edge of the spiral wall bodies and the end plates which are opposite the spiral wall bodies is provided on the top edge of the spiral wall bodies so as to protrude from the top edge of the spiral wall bodies. In general, the high pressure compressed gas near the center of the spiral wall bodies enters between the tip seal and the inside surface of the groove and reaches the gap between the bottom surface of the tip seal and the bottom surface of the groove. Then, the compressed gas applies a back pressure to the bottom surface of the tip seal and thereby the tip seal is pressed upward. Then, the tip seal provided in the top edge of the spiral wall body contacts the end plate, and it seals the border between the top edge of the spiral wall body and the end plate. In the scroll compressor comprising stepwise spiral wall bodies, for example, the tip seal provided in the spiral wall body of the fixed scroll member is divided into two parts in which one is provided at the center and the other is provided at the outer end of the spiral wall body, with respect to the step portion. Since, the pressure of the working gas in the compression chamber at the outer end of the spiral wall body is lower compared with the pressure of the working gas in the compression chamber at the center of the spiral wall body, the back pressure applied to the tip seal which is provided at the outer end of the spiral wall body is also lower than that applied to the tip seal which is provided at the center of the spiral wall body. Therefore, the seal ability is improved by making the tip seal protrude from the high top edge at the outer end of the spiral wall body in advance, and the refrigerating ability of the scroll compressor is improved.